A multiple ingredient, composite index that includes 0-6 km bulk wind
difference (6BWD), 0-1 km storm-relative
helicity (SRH1), surface parcel CAPE (sbCAPE), and surface parcel
LCL height (sbLCL). This version of STP mimics the original formulation presented
by Thompson et al. (2003) by using fixed-layer calculations
of vertical shear, and substitutes the surface lifted parcels as an alternative
to the ML parcels in the "effective layer" version of STP.

The sbLCL term is set to 1.0 when sbLCL < 1000 m, and set to 0.0
when sbLCL > 2000 m; the 6BWD term is capped at a value of 1.5 for 6BWD > 30 m s-1, and set to 0.0
when 6BWD < 12.5 m s-1.

A majority of significant tornadoes (F2 or greater damage) have
been associated with STP values greater than 1, while most
non-tornadic supercells have been associated with values less
than 1 in a large sample of RAP analysis proximity soundings.

Additional information can be found here and (Please open this
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